Earth s minerals as time integrated detectors for axions
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Earth’s Minerals as time-integrated detectors for Axions. Anastasios Liolios Physics Department Aristotle University of Thessaloniki K. Zioutas G.Kitis G.Polymeris N.Tsirliganis. Overview. Axions what are they? sources Dose Rate in matter from natural sources from axions

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Earth’s Minerals as time-integrated detectors for Axions

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Earth’s Minerals astime-integrated detectors for Axions

Anastasios Liolios

Physics Department

Aristotle University

of Thessaloniki

K. Zioutas





  • Axions

    what are they?


  • Dose Rate in matter

    from natural sources

    from axions

  • Dose measurement: TL / OSL

  • Setting limits on gaγγ

  • Conclusions


excellent candidate for dark matter

More about axions

Axion phenomenology is determined by its mass ma, which in turn is fixed by the scalefa of the Peccei-Quinn symmetry breaking:

A combination of cosmological, astrophysical and nuclear physics constraints, restricts the allowed range of viable axion masses into:

10-6 eV < ma < 10-2 eV

This range suggests a range for the coupling constant, gaγγ, which is proportional to ma :

gaγγ(GeV -1) = 10-10·ma(eV)

Axions may occur in two flavors:

  • Standard (Peccei-Quinn) Axion:

    • similar to very light neutral pion (π0)

    • rest mass ~ 10-6.. 10-2 eV/c2

    • lifetime longer than the age of the Universe

  • Kaluza-Klein (KK) Axions:

    • predicted by theories of extra-dimensions

    • mass spectrum of all the excited Kaluza-Klein states extends up to ~ 10 keV / c2

    • relative shorter lifetime: τ ~ m-3

The axion-photon-photon coupling constant gαγγ is the same for both types

Axions is expectedto be produced in the core of the stars via the Primakoff effect which converts the blackbody photons into axions in the electric field of the plasma constituents.

Galactic (relic) axions

When the Galaxy was formed, cold dark matter clustered with luminous matter.

Halo contains the most of the mass of the Milky Way, presumably in the form of cold dark matter.

Rotation curve of a spiral galaxy.

Density → ρDM ~ 0.3 GeV/cm3

Dark Matter candidates beyond the SM:

WIMPs (SS)&Axions (QCD, CP)

Relic and solar axion fluxes

Solar axions:

  • continuous spectrum

  • mean kinetic energy ~ 4.2 keV.

  • Estimated flux within the standard solar model is:

    Φsolar = 3.5·1011 ·(1010·gaγγ)2 =

    = 3.5·1011·ma2 (cm-2 s-1)

  • Dark Matter halo particles

  • (relic axions?):

    • in isothermal equilibrium

  • average velocity υ ~ 300 km/s

  • local density ρ ~ 0.3 GeV/cm3.

  • Expected flux:

  • Φrel = n·u = (ρrel /ma)·u

  • = 1016/ma (cm-2s-1)

  • Natural minerals as“dark matter dosimeters” ?

    A method for setting boundson dark matter particle characteristicsby using natural dosimeters.

    Estimation of bounds

    for the axion coupling constantgaγγ,

    usinggeological materials

    as time-integrating luminescence detectors.

    Axion Dose Rate in matter

    • The dose accumulated per unit time in a material is the Dose Rate (DR):

      DR = 1,6·10-16Φ·σ·Ν·Ε (Gy/sec) (1 Gy = 1 J/kg)


      Φi (cm-2s-1) is total flux of particles at earth,

      σ (cm2) is the total cross section of their interaction with ordinary matter,

      E (eV) is the energy of the particles, N ~ 1023 is the number of atoms/gr of earth’s matter

    axion to photon conversion

    dose accumulated in a material

    Cross Section for elastic axion to photon conversion

    (Creswick et al., Phys.Lett. B 427(1998)235)

    Total cross section for elastic axion to photon conversionin the presence of a nucleus with charge Z:

    where n = r0k, (r0 the screening length of atoms, k the photon-axion momentum).

    The first bracket is proportional to Z2 and (gaγγ)2 αnd for gaγγ= 10-8 GeV-1

    it takes the values of ~2∙10-45 cm2for Z = 14 (Si) and ~0.7∙10-45 cm2for Z = 8 (O) .

    The values of the second bracket (the coherence term) change from 1 to 10 for energy in the range above 1 keV. On the contrary, it goes down very fast for energies below 1 keV, reaching 10-9 for the energy of 1 keV.

    The cross section (per atom) integrated over the energy range 0 to 12 keV is:

    σ ≈ (10-28 cm2)∙g2aγγ ≈ (10-48 cm2)∙ma2

    or (for gaγγ = 10-8GeV-1):σ ≈ (10-44 cm2)∙

    Estimation of Dose Ratefrom solar and relic axions

    The associated Dose Rate from axions is a function of axion's coupling constant gaγγ or, alternatively, of its rest mass. Since DR is proportional to Φ and to σ (~ ma2) :

    DR ~ Φ·σ

    it will be proportional to ma4 in the case of solar axions (Φ ~ ma2) and proportional to ma in the case of galactic axions(Φ ~ 1/ma).

    Dose Rate from solar axions:

    DR≈ 10-14 ma4Gy/year

    Dose Rate from relic axions:

    DR = 5·10-18 ·maGy/year

    Estimation of Dose Rate from solar neutrinos

    • ~6·1010solar neutrinos cm-2s-1 at Earth (produced in the Sun by p-p process)

      with a mean energy of ~0.25 MeV.

    • Interaction cross section with matter:

      σ ≈ 10-47cm2Ev / MeV

      for νen→e-p or anti-νe p→e+p , . . ., inelastic (charged-current events)

    • The expected dose rate from solar neutrinos is:

      DRv≈ 10-24(Gy/sec) ≈ 3·10-17(Gy/yr)

      This is lower than the DR from solar axions for ma above ~ 0.1 eV.

       the proposed method is applicablefor ma> 0.1 eV gaγγ > 10-11 GeV-1

    Time-Integrated Luminescence Detectors

    Geologicalmaterials receive a total dose from:

    • natural radioactivity

    • cosmic rays

    • other sources (axions?)

      Apossible dose excess could be attributed to axions

       estimation of gaγγ limits

      The dose is measured by

      Thermoluminescence and Optically Stimulated Luminescence.

    natural dose

    Luminescence (TL/OSL) and Dosimetry

    Thermoluminescence (TL) or Optically Stimulated Luminescence (OSL) techniques measure the accumulated dose in a material which was exposed to radiation.

    As the material is heated or exposed to light,

    a light signal, proportional to the dose, is produced.

    Natural TL/OSL dosimeters

    • sedimentary quartz (SiO2)

    • natural Calcium Fluoride (CaF2:N)

    • feldspars (x[AlSi3O8], x = K, Na, Ca)

      problems: signal fading and high dose thresholds

    Determination of the accumulated dosesdue to the natural components of radiation

    • natural radiation sources

      • Cosmic rays

      • Natural radioactivity

        • alpha spectroscopy for the U and Th content

        • beta and gamma spectroscopy for 40K

        • gamma radiation field at the position of the sample

    • natural dose estimation from

      • the geological age of the sample

      • the average annual dose rate.

    Limitations due to “background” and TL/OSL sensitivity

    • Natural dose rate / axion dose rate

      • 105 for typical geological samples in continental crust

    • strong background suppression is needed

      • samples from deep underground (less cosmic rays)

      • pure materials(lowest possible concentrations in 40K, Th and U )

    • TL dosimetry Lowest Detectable Dose Limit (LDDL)

      • 10-4 Gy using quartz

      • 10-6 Gy, using CaF2:N

    gaγγlimits due to LDDL

    (Dose Rate)·(Stability Time Period of the TL/OSL)>(Lowest Detectable Dose Limit)

    DR·P > LDDL

    andStability Time Period of the TL/OSL signal: P < 5·108 yr

    • For quartz: LDDL ≈ 10-4 Gy → DR (limit) ≈ 0.2·10-12 Gy/yr.

      This corresponds to a solar axion mass: mα > 2.5 eV →gaγγ> 2.5·10-10 GeV-1

    • For CaF2:N: LDDL ≈ 10-6 Gy → DR (limit) ≈ 0.2·10-14 Gy/yr.

      The method could detect doses from solar axions

      with mass ma > 1 eV →gaγγ > 10-10 GeV-1

      Assumption: ideal TL/OSL samples

       no contribution from natural radioactivity

       no contribution from cosmic rays

    Two real sample examples

    • KOUPA sample (quartz)

      • Natural U concentration 60 ppb

      • 232Th concentration 86 ppb

      • 40K concentration < 0.005 %

      • Cosmic dose rate 1.8·10-4 Gy/year

      • Total dose rate ~ 1.8·10-4 Gy/year

      • gaγγ best limit4·10-8 GeV-1

    • NESTOR sample (quartz)

      • Natural U concentration 4 ppm

      • 232Th concentration 6 ppm

      • 40K concentration < 1.16 %

      • Cosmic dose rate < 10-9 Gy/year

      • Total dose rate ~ 1.7·10-3 Gy/year

      • gaγγ best limit 7·10-8 GeV-1


    • A method was presented for setting bounds on dark matter particle characteristics by using geological materials as natural dosimeters.

    For solar axions:

    • Assuming no contribution from natural radioactivityand cosmic rays, the method sets the best limits to

      gaγγ = 10-10 GeV-1 using natural CaF2

      gaγγ = 2.5·10-10 GeV-1 using SiO2

    • Using real samples, the feasible limits are

      gaγγ= 4·10-8 GeV-1 (KOUPA samples)

      gaγγ= 7·10-8 GeV-1 (NESTOR samples)

    • A search for better natural TL/OSLsamples is needed in order to improve the above limits

      “Minerals as Time-Integrating Luminescence Detector for setting bounds on Dark Matter Particles Characteristics” NIM A in print

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